Fundus imaging is a part of basic eye exams, yet the size, cost and complexity of conventional retinal cameras limit the availability of fundus imaging for screening, field diagnosis, and progress monitoring of many retinal diseases. Wide-field fundus imaging is difficult due to the low reflectivity of the fundus, the small eye pupil size, and the high background noise from corneal and iris reflections. Most commercial wide-field fundus cameras employ complex optical designs to image the fundus while avoiding corneal and iris reflections, which require precise lateral and axial alignment of the camera to the patient's pupil.
In both table-top and portable realizations of conventional fundus cameras, fundus imaging usually requires either pupil dilation using dilation agents or a trained operator aided with infra-red imaging for the alignment. There are automated systems that utilize closed-loop optomechanical feedback for camera alignment, but still suffer from large system size and cost, as well as, a slow alignment process.
Recently, a self-imaging portable retinal camera has been developed using a separate fixation path with a set of pinhole masks placed near and on the conjugate plane to the retina that confine the ray angles. However, this design suffers from a small imaging field-of-view compared to state-of-the-art commercial systems and the self-alignment scheme is based on pupil-forming pinhole masks, which result in a low imaging yield.